The present invention generally relates to air bags and more specifically to an air bag useful in a rollover accident.
The prior art has recognized a need for an air bag useful in a side impact accident. One such side impact air bag is stored at or near the roof rail of the vehicle. This type of air bag is typically long and narrow in construction and, when deployed, extends from the roof rail to approximately shoulder height and is designed primarily to protect the head of the occupant from impacting the window and/or side of the vehicle. Some air bags extend from the front or A-pillar, across a middle or B-pillar, to a rear C and/or D-pillar of the vehicle. U.S. Pat. No. 6,074,961 is typical of a side impact, curtain air bag. As can be seen, the air bag includes a forward and rear inflatable volume and a central non-inflated, inactive zone, which is typically located proximate a non-occupied region of the vehicle such as the B-pillar. In a typical side impact accident, the entire accident lasts less than 100 milliseconds and during that time the air bag must inflate, position itself between the occupant and the side of the vehicle and deflate.
The construction of a curtain air bag that is designated to protect an occupant during a vehicle rollover is substantially identical to the construction of a side impact air bag. The basic difference is that care must be taken in the design to insure that the air bag retains a sufficiently high pressure for relatively long periods of time (as a rollover accident takes many seconds to complete). This inflation period is equal to or greater than, for example, five to seven seconds, as the air bag must remain inflated for this longer time to protect the occupant at the end of end of the longer, rollover event. Even if the material used to construct the air bag is made from low or even zero permeability material, a certain amount of inflation gas may leak through any sewn seam, tending the reduce the pressure within the air bag. Even if the bag uses zero permeability material and does not utilize any sewn seam, the pressure within the air bag will reduce as the inflation gas cools. The internal pressure may also be reduced because the fabric has been stretched creating a larger volume. To compensate for this reduction in pressure over an extended time period it has been proposed to over inflate the air bag typically using a high capacity inflator. The effect of using the higher capacity inflator and over inflating the air bag is to produce an air bag or cushion that is relatively stiff and more resilient and which may act as an air spring. Consequently, during the initial moments of a side impact or rollover accident, the occupant""s head may rebound off of this stiff cushion, which may result in a high HIC level in excess of 900.
It is an object of the present invention to provide a rollover curtain air bag that is capable of maintaining an adequate pressure for an extended period of time but without causing such high HIC injury levels.
It is a further object of the present invention is to provide an air bag with an accumulator pocket, which controls the resiliency of the inflatable portions of the air bag.
Accordingly the invention comprises: a rollover air bag system comprising: at least a first inflatable first chamber, the air bag adapted to be mounted within a passenger compartment of a vehicle in a manner such that when the air bag is inflated the first inflatable chamber is positioned to receive and protect the head of an occupant, an accumulator chamber in communication with the first chamber, the accumulator chamber initially maintained at a negative pressure relative to the inflated or partially inflated first chamber, wherein in order to restrict the pressure in the first chamber from increasing upon impact with a body part of the occupant, the inflation gas in the first chamber is allowed to flow into the accumulator chamber. In one embodiment the air bag extends between at least two vehicle pillars and can extend across all of the vehicle pillars. In another embodiment the air bag is substantially smaller and blocks interaction between the occupant and the side of the vehicle, which may include a single pillar or the roof rail or window area.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.